1. Technical Field
This disclosure relates to a secondary-battery maximum-capacity measuring apparatus. For details, this disclosure relates to an apparatus for measuring the maximum capacity of a secondary battery even during the use of the secondary battery.
2. Related Art
A secondary battery, which allows repetitive charge, is used as a power supply for driving a running motor for a hybrid vehicle, an electric vehicle, or similar vehicle. The secondary battery can store energy with a comparatively small environmental load, for example, energy generated by the sun or energy generated by wind power without relying on fossil fuel. Accordingly, there is a growing broad use of the secondary battery in, for example, industry, public institutions or standard homes.
Generally, these secondary batteries are each configured as a battery module for obtaining a desired output voltage by coupling the predetermined number of battery cells together in series. The secondary battery is configured as a battery pack for obtaining a desired current-carrying capacity (Ah) by coupling the predetermined number of the battery modules for obtaining the desired output voltage together in parallel.
For example, the secondary battery mounted on an automobile as a driving power supply for a running motor is considered to mainly employ a lithium-ion battery for the time being for the convenience of charging time, cruising distance, and similar matter.
Now, one of indexes representing the performance of the secondary battery is the maximum capacity of the battery. This maximum capacity can be defined as an electric quantity (Ah) output while an open cell voltage of the battery decreases from the maximum voltage to the available minimum voltage.
FIG. 16 is a block diagram illustrating one example of a conventional secondary-battery maximum-capacity measuring apparatus that measures the maximum capacity of a secondary battery in use. In FIG. 16, a current sensor 1 measures a current flowing through the secondary battery (hereinafter referred to as DUT) in use. A voltage sensor 2 measures an inter-terminal voltage of the secondary battery DUT in use.
A ΔQ calculation unit 3 integrates current values measured by the current sensor 1 so as to obtain an electric quantity ΔQ that has flowed through the DUT during a certain period of time.
An OCV calculation unit 4 uses voltage values measured by the voltage sensor 2 and current values measured by the current sensor 1 to obtain an open cell voltage OCV of the DUT during a certain period of time.
A ΔSOC calculation unit 5 uses the open cell voltage OCV obtained by the OCV calculation unit 4 to obtain a change ΔSOC in state of charge SOC during a certain period of time. Here, the state of charge SOC can be obtained by using a known relationship between the state of charge SOC and the open cell voltage OCV.
A battery capacity measuring unit (maximum capacity measuring unit) 6 obtains the maximum capacity Q′max of the DUT with the following formula.Q′max[Ah]=ΔQ[Ah]×100[%]/ΔSOC[%]
A display unit 7 displays the maximum capacity Q′max measured by the battery capacity measuring unit 6 on, for example, a liquid crystal display.
JP-A-2009-71986 discloses a technique for determining a degree of deterioration of an on-vehicle battery without complicated computation.